Interferometric synthetic aperture microscopy (ISAM) is a method of tomographic optical microscopy that brings the power of computed imaging and inverse scattering together with interferometric broadband optical imaging. ISAM provides spatially invariant resolution of objects in an extended 3-D volume including regions away from the focus of the objective and quantitative estimation of the inhomogeneities in refractive index or susceptibility of an object. The solution of the inverse problem for ISAM has been found for many scanning geometries and types of illumination, including low-numerical aperture scanned-beam (see Ralston et al. “Inverse scattering for optical coherence tomography,” J. Opt. Soc. Am. A, 23, pp. 1027-37 (2006), hereinafter Ralston (2006)), high numerical aperture scanned-beam (see Ralston et al., “Inverse scattering for high-resolution interferometric microscopy,” Opt. Lett., 31, pp. 3585-87 (2006), hereinafter Ralston (2006a)), rotationally-scanned beam catheter (see Marks et al., “Inverse scattering for rotationally scanned optical coherence tomography,” J. Opt. Soc. Am. A, 23, pp. 2433-39 (2006)), and full-field illumination (see Marks et al., “Inverse scattering for frequency-scanned full-field optical coherence tomography,” J. Opt. Soc. Am. A, 24, pp. 1034-41 (2007)). The latter reference will be referred to hereinafter as Marks (2007), and all of the foregoing articles are incorporated herein by reference.
In prior treatments, while the illumination source may be temporally incoherent, or broadband, a spatially coherent (single mode) illumination source was assumed. In general, however, illumination sources in microscopy are, in fact, spatially partially coherent, as discussed, for example, in Mandel & Wolf, Optical Coherence and Quantum Optics, (Cambridge University Press, 1995), which is incorporated herein by reference. Solutions derived in prior treatments that assumed a single spatial mode are thus inapplicable to the case of illumination by partially coherent sources.